This invention relates to a circuit for controlling the characteristics of the electrical current to any load requiring sinusoidal waveforms at any power level. One such application is for AC corotrons used in commercial xerographic machine hardware.
Historically, such AC corotrons have been supplied from a constant voltage transformer operated in an overloaded condition and controlled with a shunt regulator. This provides a variable amplitude sine wave which can be electrically controlled. This has been done commercially in the past in both the model 3100 and 4000 xerographic processors manufactured and marketed by Xerox Corporation. The constant voltage transformer is a relatively expensive item as is the power supply.
Another prior art type of power supply involved a series pass transistor in the primary winding of a standard transformer. This greatly reduces the cost of a given output bit it distorts the sine wave greatly by effectively chopping off the upper parts of the waves. This could create a problem in xerographic machines since these machines are typically RMS sensitive to a wave shape rather than to the amplitude of a wave. Thus, the clipping off of the top of the wave changes the RMS to average ratio. But since power supplies most easily recognize the average value of a wave, there are problems in making the RMS value track with the average value of the output of the power supply. Therefore, the regulation that is apparent to the machine is not as good as if a good sine wave had been utilized.